1. Technical Field
The present invention relates to an electronic component mounting structure.
2. Related Art
Technologies for mounting an electronic component, such as a semiconductor IC, on a substrate have been used in the process of manufacturing circuit substrates or liquid crystal displays to be mounted on various electronic apparatuses. For example, a liquid crystal-driving IC chip for driving a liquid crystal panel is mounted on a liquid crystal display. Such a liquid crystal-driving IC chip may be directly mounted on a glass substrate to be included in a liquid crystal panel. Also, such a liquid crystal-driving IC chip may be mounted on a flexible substrate (FPC) to be mounted on a liquid crystal panel. The former mounting structure is called a COG (chip on glass) structure, and the latter is called a COF (chip on FPC) structure. In addition to these mounting structures, a COB (chip on board) structure where an IC chip is mounted on a glass-epoxy substrate or the like is also known.
On a substrate used in such a mounting structure, a land (terminal) connected to a wiring pattern is formed, while on an electronic component, a bump electrode for obtaining electrical connection is formed. By mounting the electronic component on the substrate in a state where the bump electrode is connected to the land, an electronic component mounting structure is formed.
Incidentally, in the above-mentioned mounting structure, it is desirable that the electronic component be connected onto the substrate more firmly and reliably. In particular, if the substrate and electronic component include multiple lands and multiple bump electrodes, respectively, and the lands and the corresponding bump electrodes are connected to each other, it is important that all the lands and the corresponding bump electrodes are favorably connected to each other, in order to ensure reliability.
However, typically, lands and bump electrodes are each made of a metal. Therefore, if misalignment occurs when joining these electrodes together or misalignment occurs between these electrodes since the positioning accuracy of the lands and bump electrodes is low, sufficient bonding strength between the lands and bump electrodes is not obtained. Thus, there is a possibility that a contact failure (electrical connection failure) will occur.
Also, warpage in the substrate or the electronic component, such as an IC, or unevenness in the height of the formed lands, bump electrodes, or the like makes inconsistent the distances between the lands and bump electrodes. For this reason, sufficient bonding strength between the lands and bump electrodes is not obtained and there is a possibility that a contact failure (electrical connection failure) will occur.
In order to prevent such a problem, there have been provided printed wiring boards where a conductive pattern having a trapezoidal section is provided, a metal conductive layer is formed on the conductive pattern, and many recesses and protrusions are made on a surface of the metal conductive layer (for example, see JP-A-2002-261407).
It is believed that, by using such a printed wiring board, an anchor effect obtained by the recesses and protrusions on the surface of the metal conductive layer prevents slides of the connection electrodes of the component (electronic component) on the electrodes of the substrate, fall and inclination of the connection electrodes, or the like even if pressure is applied to the component when mounting the component, and thus the mounting yield is increased.
However, even the printed wiring board having the above-mentioned advantage does not have a structure where the bonding strength between a connection electrode and a substrate electrode is increased and, further, the bonding strength between multiple connection electrodes and substrate electrodes is increased. Therefore, if misalignment occurs at the time of joining these electrodes together or misalignment occurs between these electrodes since the positioning accuracy between these electrodes (between the lands and bump electrodes) is low, sufficient bonding strength between these electrodes is not obtained and there remains a possibility that a contact failure (electrical connection failure) will occur. Also, since the connection electrodes (bump electrodes) are made of a metal, the connection electrodes become deformed plastically when connected to the lands. Therefore, the connection electrodes are lacking in the capability of, if the distances between the lands and bump electrodes are made inconsistent as described above, absorbing the distance changes by becoming deformed elastically. For this reason, sufficient bonding strength between these electrodes is not obtained, and there remains a possibility that a contact failure (electrical connection failure) will occur.
Also, in the above-mentioned joining structure (mounting structure) between the printed wiring board having the metal conductive layer and the component including the connection electrodes, a bonding material, such as an underfill material, is required to mount and fix the component on the printed wiring board. This is a factor that prevents a reduction in the cost required for mounting.